Constant amplitude phase shifter

ABSTRACT

In many color television circuitry designs, a 3.58 mHz reference signal is provided to the automatic phase control phase detector and the color killer phase detector, and in a closed loop color synchronization circuit, the reference signal to the color killer detector is shifted in phase 90* relative to the automatic phase control detector. In addition, harmonics of the reference signal and color burst signal must be controlled. Further, in many circuits an adjustable phase section is added to adjust the phase of the reference signal to the automatic phase control detector and the color killer detector for tint control. This invention provides circuitry which will bypass the harmonics to ground and compensate for the impedances of such harmonic bypass circuit and the color killer detector fixed phase shifter and provides a substantially constant amplitude to the phase detectors for all positions of the adjustable phase shift circuit. In a preferred embodiment, an equivalent resistance is uniquely determined and the impedance of a harmon bypass circuit and the fixed phase shift device of the color killer detector is made substantially equal to this equivalent resistance to provide the constant amplitude signal to the detectors.

United States Patent Kresock 1 CONSTANT AMPLITUDE PHASE SHIFTER [72]Inventor: John M. Kresock, Fort Wayne, Ind.

[73] Assignee: The. Magnovox Wayne, Ind.

[22] Filed: May 11, 1970 [21] Appl. No.: 36,018

Company, Ft.

[52] US. Cl. ..l78/5.4 CK, l78/5.4 SY, 323/122, 323/125, 178/5.4 HE

[51] Int. Cl. ..H04n 9/44, H04n 9/48 [58] Field of Search ..l78/5.4 HE,5.4 R, 5.4 CK, l78/5.4 SY, 69.5 CB; 307/262; 328/155,

Primary Examiner-Robert L. Richardson Attorney-Richard T. Seeger 51Sept. 26, 1972 [57] ABSTRACT in many color television circuitry designs,a 3.58 ml-lz reference signal is provided to the automatic phase controlphase detector and the color killer phase detector, and in a closed loopcolor synchronization circuit, the reference signal to the color killerdetector is shifted in phase 90 relative to the automatic phase controldetector. In addition, harmonics of the reference signal and color burstsignal must be controlled. Further, in many circuits an adjustable phasesection is added to adjust the phase of the reference signal to theautomatic phase control detector and the color killer detector for tintcontrol. This'invention provides circuitry which will bypass theharmonics to ground and compensate for the impedances of such harmonicbypass circuit and the color killer detector fixed phase shifter andprovides a substantially constant amplitude to the phase detectors forall positions of the adjustable phase shift circuit. in a preferredembodiment, an equivalent resistance is uniquely determined and theimpedance of a harmon bypass circuit and the fixed phase shift device ofthe color killer detector is made substantially equal to this equivalentresistance to provide the constant amplitude signal to the detectors.

3 Claims, 3 Drawing Figures 22 F AUTO PHASE CONTROL I PHASE DETECTOR cw3.58MH 2 REFERENCE SIGNAL GENERATOR "wk rk COLOR KILLER A v I L2 1 JPHASE DETECTOR ==cs m cs R3 I g I PATENTEllsiPzs 1972 AUTO PHASE CONTROLPHASE DETECTOR COLOR KILLER PHASE DETECTOR CW 3 58MH REFERENCE SIGNALGENERATOR CURRENT l GENERATOR REAL COMPONENT OF ADMITTANCE JOHNM.KRESOCK INVENTOR, M://\ [\A ATTORNEY IMAGINARY COMPONENT OF ADMITTANCEADMITTANCE DIAGRAM FIG 3 In color television circuits having a closedloop color synchronization circuit with a synchronous color killer, itis required that the 3.58 mI-lz reference signal to the color killerdetector lead or lag signal to the automatic phase control detector by90. In addition, it is desirable that the harmonics which are generatedby the CW oscillator supplying the I reference signal to the automaticphase control detector and the color killer detector, and the colorburst harmonics from these latter detectors'be' controlled sinceharmonics cause beats,

especially during low signal strength. In certain circuits, includedwithin the scope of this invention, it is also desirable to haveanadjustable phase shift to adjust the phaseflof the'reference signalgoing'to the automatic phase control detector and'the color killerdetector. As

.isknown in .the art, it ishighly desired to have the amplitude of thereference signal going to these detectors substantially constant overall ranges of operations and inorder to accomplish this, and at the sametime provide a constant phase shift to the color killer detector circuitand control the harmonics, and provide an adjustable phase shift to thedetectors, presents a problem not heretofore solved.

This invention overcomes and provides a solution for these problems byteaching the manner and means of circuit" design which satisfactorily"provides the im- "pedances of the harmonic bypassand fixed phase shiftcircuits under the wide variations of phase adjustments to provide asubstantially constant amplitude reference signal to the color killerand automatic phase control detector circuits while providing a.circuitfor bypassing the harmonics to ground. The manner in which this solutionis carried out in a preferred embodiment later described is to provide acapacitor so placed as to pass harmonics to ground and provide anequivalent resistance which is determined in a novel manner and then tomake the impedance of the constant phase shift circuit for the colorkillerdetect'o'r arid the capacitors which bypass the harmonics toground substantially equal tothis equivalent resistance. This equivalentresistance is determinedby plotting the admittance of a variable phaseshift circuit over a range of phase variations and plotting the locus ofthese admittances as the adjustable phase shift control is varied. Inthis preferred embodiment, once this locus has been determined, theradius of the arc is graphically found and is compared with theadmittance of circuit G when this admittance is entirely real orthatvalue where j equals zero, and the equivalent resistive admittance of Ris equal to the difference between the radius and the admittance of thevariable phase shift circuit at the j equals zero point. These and otherobjects and advantages will become more apparent when the above referredto preferred embodiment is considered in connection with the followingdrawings.

DRAWINGS FIG. 1 is a schematic showing the circuitry between thereference signal and the automatic phase control phase detector and thecolor killer phase detector with the constant phase shift circuit, theharmonic bypass capacitors, and the adjustable phase shift circuitplaced therebetween;

FIG. 2 is a schematic showing the circuitry for dedeterminingthe valueof R; or the equivalent resistance; I

FIG. 3 is an admittance vector diagram plotted according to the datataken from the circuit of FIG. 2 and indicating the vector constructionfor determining R DETAILED DESCRIPTION 7 In'FIG. l is shown a referencesignal generator 21 which could be typically a pentode section of a 6GH8CW oscillator tube, the plate of which is connected to resonant circuit22,-which resonates at 3.58 mil and which sends a sinusoidal signalthrough capacitor C: which provides a highjimpedance compared to theimpedance of the circuit'following C, including phase detectors 24, 25so'that the current at Point A is substantially capacitive and at asubstantially constant amplitude. I

This invention provides a capacitor C between Point A and ground to passsubstantially all of the harmonics coming from the color referencesignal means 21. Connected to Point A is a color killer phase shiftcircuit 23 comprising an inductance L connected to Line B-and acapacitance C connecting Line B to ground and a resistance R connectingLine B to ground. From Line B, the signal goes through R, to the colorkiller phase detector 24 of a closed loop synchronization circuit whichis well known in the art.

L, provides a high-impedance to harmonics from the color killer phasedetector 24 and C is low impedance to ground for these same harmonics sothat any harmonies coming from the detector 24 tend to be shunted toground through C Circuit 23 provides a lag of the signal to the detector24 and yet maintains a one to one signal amplitude across L Alsoconnected to Point A voltage is Resistor R which passes the fundamentalsignal to automatic phase control phase detector circuit 25 which alsois a part of the closed loop color synchronization system above referredto'and well'known inthe art.'The automatic phase control phase detectorcircuit 25 also emits color, burst harmonics which are passed to groundthrough C Therefore, C acts to pass harmonies of the referencefundamental emitted by the reference signal 21, and harmonics of thecolor burst fundamental emitted by automatic phase control phasedetector 25 and the color killer phase detector 24.

Also connected to the signal at Point A is the circuit containingresistance R inductance L variable resistance R and capacitance C Thiscircuit provides a means of varying the phase of the fundamental signalto detectors 24, 25 by varying the resistance of R This variation ofphase is desirable to vary the hue of the signal on the televisionreceiver, but its use, and the use of capacitor C together with elementsL C and R present unusual problems in maintaining a constant amplitudesignal to detectors 24, 25. The following means have been devised toovercome these problems.

In FIG. 2 is shown circuitry and FIG. 3 is shown a diagram showing thedevelopment of circuit parameters to solve the above problems. In FIG. 2is shown a current generator 26 which is the equivalent of generator 21,circuit 22, and capacitor C of FIG. 1. Generator 26 is connected to thecircuit having resistance-R inductance L capacitance C, and resistance RElements R,, L,, C,, and R correspond to the elements correspondinglymarked in FIG. 1. R is shown in dashed lines and is the value beingdetermined and is substantially the equivalent resistance of the loadprovided to the circuit by L C R and C R is shown only to indicate whereit would be in relation to circuit G once R has been determined. Byvarying R and plotting the phase angle (which is determined by value ofR of the circuit G v. the magnitude of the admittance of the circuit Gshown in FIG. 2 taken at terminals E and F, obtains are 27 which is alocus of the admittances of Y as the admittance of R is varied from zeroto infinity. The approximate center 28 for .the arc'27 is determinedgeometrically and the radius R of are 27 is then compared with theadmittance of circuit G at the zero line and the difference Y betweenpoint 28 and point 29 is the admittance of R From this R is determinedand through methods known to the art, such as set forth in the textentitled Electrical Engineering Circuits, 2d Edition, by Hugh HildrethSkilling, published by Wiley, the equivalent load resistance of elementsC L C and R, can be made equal to R R, is selected to place limits onthe phase range that can be obtained by adjusting R In the presentinstance, range is approximately :45 from the central setting and isthat angle measured at 28.

The load of phase detectors 24, 25 may be neglected in the computationof the equivalent resistance of ele ments C L C and R since the load isof small consequence in determining the amplitude of the signals at lineB and point A.

R, and'L, are designed'to restrict harmonic flow and C, is the cablecapacitance of the R cable, but if any harmonics do get through R, andL,, they are bypassed to ground through C In the preferred embodimentdisclosed, the components may have the following values:

C 12 pf C, I00 pf C, lOO pf C, 39 pf R 82 ohms R 100 ohms R l.l K-ohmsR, 100 ohms R 1.2 K-ohms L, 5.6 uh

L 47 uh It will be understood that modifications and variations may beeffected without departing from the spirit and scope of the novelconcepts of this invention.

lclaim:

1. Apparatus comprising input means,

output means,

constant phase shift means,

said constant phase shift means being between said input means andoutput means to provide a fixed adjustment of the phase of a signaltherebetween, shunt means for shunting away predetermined unwantedsignals from both said input means and output means, variable phaseshift means for providing a variable adjustment of the phase betweensaid input and out ut e s the sli m o t eadmittances of said constantphase shift means, said shunt means and said variable phase shift meansbeing-substantially equal at a plurality of phase shift positions.

2. Constant amplitude phase shift circuit comprising input means forproviding a fundamental signal, I

output means comprising a first and second output for receiving thefundamental signal,

constant phase shift means including inductance, capacitance, andresistance means for providing a constant phase shift of the fundamentalto said second output,

bypass means for bypassing to ground harmonics from both said inputmeans and output means,

variable phase shift means for providing a variable adjustment of thephase between said input and output means,

the sum of the admittances of said constant phase shift means, saidharmonic bypass means and said variable phase shift means beingsubstantially equal at a plurality of phase shift positions.

3. Constant amplitude phase shift circuit comprising automatic phasecontrol phase detector,

color killer phase detector,

CW oscillator for providing a reference signal to said automatic phasecontrol phase detector and the color killer phase detector,

phase shift means comprising means for shifting the phase of thereference signal to the color killer phase detector substantially fromthe phase provided to the automatic phase control phase detector,

capacitor means for bypassing to ground harmonics from both of saidphase detectors and from said CW oscillator,

variable phase shift means for variably shifting the phase of thereference signal to both of said phase detectors,

the admittance of the equivalent resistance of said phase shift meansplus said capacitor means being substantially equal to that admittancerequired to be added to the admittance of the variable phase shiftcircuit to provide a substantially constant amplitude admittance for thecombination of said phase shift means, variable phase shift means andcapacitor means over the phase shift range of said variable phaseshifter to provide a substantially constant amplitude signal to saidautomatic phase control and color killer phase detectors over the rangeof phase shift of said phase shift means.

1. Apparatus comprising input means, output means, constant phase shiftmeans, said constant phase shift means being between said input meansand output means to provide a fixed adjustment of the phase of a signaltherebetween, shunt means for shunting away predetermined unwantedsignals from both said Input means and output means, variable phaseshift means for providing a variable adjustment of the phase betweensaid input and output means, the sum of the admittances of said constantphase shift means, said shunt means and said variable phase shift meansbeing substantially equal at a plurality of phase shift positions. 2.Constant amplitude phase shift circuit comprising input means forproviding a fundamental signal, output means comprising a first andsecond output for receiving the fundamental signal, constant phase shiftmeans including inductance, capacitance, and resistance means forproviding a constant phase shift of the fundamental to said secondoutput, bypass means for bypassing to ground harmonics from both saidinput means and output means, variable phase shift means for providing avariable adjustment of the phase between said input and output means,the sum of the admittances of said constant phase shift means, saidharmonic bypass means and said variable phase shift means beingsubstantially equal at a plurality of phase shift positions.
 3. Constantamplitude phase shift circuit comprising automatic phase control phasedetector, color killer phase detector, CW oscillator for providing areference signal to said automatic phase control phase detector and thecolor killer phase detector, phase shift means comprising means forshifting the phase of the reference signal to the color killer phasedetector substantially 90* from the phase provided to the automaticphase control phase detector, capacitor means for bypassing to groundharmonics from both of said phase detectors and from said CW oscillator,variable phase shift means for variably shifting the phase of thereference signal to both of said phase detectors, the admittance of theequivalent resistance of said phase shift means plus said capacitormeans being substantially equal to that admittance required to be addedto the admittance of the variable phase shift circuit to provide asubstantially constant amplitude admittance for the combination of saidphase shift means, variable phase shift means and capacitor means overthe phase shift range of said variable phase shifter to provide asubstantially constant amplitude signal to said automatic phase controland color killer phase detectors over the range of phase shift of saidphase shift means.